328 MM. Strove and Dollen on the Correction 



that work contains a detailed account of the method of cal- 

 culation employed ; and the summing up on page 664 shows 

 for fifteen places the amount of deflection of the plumb-line, 

 in the direction of the meridian, caused by the inequalities 

 of the surrounding country. But it is to be regretted that 

 later, page 770, the comparison of the observed latitudes 

 with those deduced from the combination of the various arcs 

 is given for only nine of these places, and not for all the fifteen ; 

 which might have been done, even if all these latitudes were 

 not used for the determination of the best mean figure of the 

 earth. We were very near trying to remedy this difii- 

 ciency, by which available material is so notably diminished, 

 by the help of data elsewhere supplied in the work itself. 

 On further reflection however we refrained from this under- 

 taking, on the ground that, in a matter in which an intimate 

 acquaintance with all the accompanying circumstances is 

 essential, it is hazardous to go further than the author himself 

 has done. We take it therefore to be the wisest way to repose 

 upon what has been given in the work itself as the result of the 

 investigations, especially as this result is arrived at so fre- 

 quently and so harmoniously as we find it stated in different 

 places in this work. The conclusions may be summed up in 

 the following three propositions : — 



1. If the observed latitudes are corrected according to the 

 amount of disturbance shown by levelling, they still do 

 not harmonize by any means entirely with those cor- 

 responding to the general figure of the earth ; but di- 

 vergences still remain which are much too great to be 

 explained by unavoidable errors of observation. 



2. But the agreement of the corrected latitudes is notably 

 greater than that of the uncorrected. 



3. On the other hand, the agreement will be none the 

 greater the further the contours are extended. 



" To understand this last proposition we must add, with 

 reference to Airy's hypothesis above mentioned, that for the 

 greater number of points which were contoured a two-fold 

 value of the deflection of the plumb-line is deduced. These, 

 which we may call A and B, are distinguished from each 

 other, the levelling in the case of B being extended to much 

 greater distances from the station than in the case of A. 

 A is therefore only a part of B, representing what is due 

 to that part of the mass nearest to the station. The third 

 proposition says that A agrees more closely with the cor- 

 rection demanded by the general figure than B does. 



" It is evident that such a fact, did it only rest on sufficient 

 grounds, would have a decided bearing on the question before us. 



